Throughout this disclosure, various publications, patents and published patent specifications are referenced by an identifying citation. Also within this disclosure are Arabic numerals referring to referenced citations, the full bibliographic details of which are provided immediately preceding the claims. The disclosures of these publications, patents and published patent specifications are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Loss of non-regenerative, terminally differentiated cardiomyocytes (CMs) is irreversible; myocardial repair is further hampered by a severe shortage of donor cells and organs. CMs can be differentiated from human (h) embryonic stem cells (ESCs) that can propagate indefinitely in culture while maintaining their pluripotency (Kehat, I. et al. (2001) The Journal of Clinical Investigation 108:407-414; Mummery, C. et al. (2003) Circulation 107:2733-2740; Pera, M. F. et al. (2000) Journal of Cell Science 113(Pt 1):5-10; Thomson, J. A. et al. (1998) Curr. Top Dev. Biol. 38:133-165; Xue, T. et al. (2005) Circulation 111:11-20; Thomson, J. A. et al. (1998) Science 282:1145-1147; Reubinoff, B. E. et al. (2000) Nat. Biotechnol. 18:399-404; Xu, C. et al. (2002) Circ Res. 91:501-508; He, J. Q. et al. (2003) Circ. Res. 93:32-39). Therefore, hESCs can provide an unlimited ex vivo source of CMs for clinical application and drug testing. While existing efforts mostly focus on the derivation of heart cells from hESCs, it is imperative that these derived CMs are functionally mature in ways similar to their adult counterparts before the desired therapeutic outcome can be achieved. In fact, hESC-CMs exhibit embryonic- or fetal-like electrophysiological properties (Mummery, C. et al. (2003) Circulation 107:2733-2740; He, J. Q. et al. (2003) Circ. Res. 93:32-39; Satin, J. et al. (2004) J. Physiol. 559:479-496). For instance, hESC-derived ventricular CMs exhibit spontaneously firing action potentials (AP), in contrast to the normally quiescent-yet-excitable phenotype of adult. Indeed, it was previously demonstrated that transplantation of a node of electrically-active hESC-CMs, consisting of a mixture of ventricular, atrial and nodal cells, could collectively serve as a surrogate pacemaker in vitro and in vivo (Xue, T. et al. (2005) Circulation 111:11-20). Thus, immature hESC-CMs are potentially arrhythmogenic after transplantation. Moreover, there is a need to develop protocols for rescuing the immature phenotypes for their eventual clinical and other applications (e.g., cardiotoxicity screening and heart disease models that accurately reflects the adult heart). This disclosure satisfies this need and provides related advantages as well.